The present invention relates to the sequential feeding of discrete items to processing machines. More particularly, the invention relates to internally synchronized discrete item feeding systems which provide accurate and efficient item registration and delivery at fast item delivery speeds.
Product feed systems are well known, and are in widespread use for the delivery of products in industrial processes. Such systems have been found to be particularly useful in conjunction with packaging machinery wherein discrete product units are delivered to machines which wrap, or otherwise process, the discrete product into a finished package for market. One form of this commercial operation involves a machine known as a horizontal-form-fill-seal machine. That machine includes an infeed conveyor which feeds products into the machine. The delivered product is then enwrapped in a tube of wrapping material that is formed by the wrapping machine, both ends and the bottom lap (or side joining of material) are sealed, and the tube of material with products within is severed between the end seals of succeeding packages to produce a series of discrete packages.
As the speed of delivery of products to the packaging machines is increased in an attempt to improve the efficiency of plant operations and reduce costs, it becomes necessary to utilize a continuous motion of the transverse sealing mechanism. These mechanisms are usually comprised of sealing jaws that rotate, or sealing jaws that travel in an orbital motion, or multiple sealing jaws fastened to a chain. In all cases the sealing jaws travel downstream at nearly the velocity of product flow during the time the transverse seal is being made. Higher packaging speeds require that the motion of the sealing jaws be essentially continuous to avoid the shock and vibration that would result from starting and stopping the jaws for each package.
Because the motion of the jaws is predetermined and continuous, it is necessary to control the location of the products entering the wrapping machine, and a flighted infeed conveyor is commonly used to control the position of products as they enter the seal jaws in a horizontal form-fill-seal machine. This is because the location of product passing through the wrapping machine must be such that the transverse jaws will make their end seals in the gaps between the products. As operational speeds become higher and product spacing becomes tightened, the location of the gaps (or spacing) between the discrete packages cannot be assured in the absence of a physical locating means such as that provided by the flights of the flighted conveyor. It should be noted, however, that even if the flighted conveyor were replaced with a flat belt conveyor, it would still be essential to control the placement of product on the belt in order to make seals in the gaps between the products. In this case, the synchronizing system of the present invention would serve the same function of locating the products into the machine as would the flighted conveyor were it present.
Feeding product between the flights of the flighted infeed conveyor has always been a problem. The simplest product feed system, of course, is manual placement of the individual product units on the conveyor. Even with multiple operators handling product to fill the flights on the conveyor, however, it is virtually impossible to keep up with a processing machine operating at well over 100 products per minute using the manual feed system.
Known mechanical feed systems for packaging machines include hopper feeds in which each flight of the conveyor strips a product off the bottom of a stack of products, and motorized hoppers which deposit product discretely into the respective spaces between the flights of the conveyor in response to signals generated by a cam or similar mechanism associated with the drive of the flighted conveyor. Such systems are limited in the types of packages which they can handle effectively. Thus, the hopper system is generally adaptable only to regularly shaped products of relatively low profile such as uniform size boxes or the like. Similarly, the motorized version is generally used to deliver thin product such as greeting cards, magazines, LP records and the like. Further, each of the hopper systems requires one product to slide along the surface of an adjacent product during the conveyor loading sequence which can cause jamming of the machinery and damage to sensitive products. Still further, manual or machine loading of the hopper is still required which introduces increased cost and reduced efficiency to the overall production operation.
Other mechanical means for sequentially loading the respective spaces between the flights of a flighted conveyor have been used. These means include angle feed in which product is fed at approximately a right angle to the flighted conveyor travel, brought to a dead stop and peeled off by the transverse action of the flights of the conveyor; the produce placement system in which the product is delivered in line against a stop which is periodically removed to permit the advance of a single product; and, timing screws which are adapted to feed product, usually of a particular shape which permits the entrance of the thread of the timing screws between adjacent product units, to the spaces between the flights of the conveyor sequentially. All of these systems have utility related to their particular mode of operation, but they all also suffer from disadvantages. In particular, the product placement system is limited to the delivery of product at speeds well below those that can be achieved with the present invention, and even at lower speeds, product motion involves violent starts and stops. Timing screws can be disadvantageous in that their use can be limited by product shape as described above, and in that a specific set of screws is required for each specific size and shape of product. The angle feed is limited to relatively narrow product, because the stop-start-stop action that occurs as each product is peeled off by the flighted conveyor and the next product is rapidly advanced into the path of the flights becomes more violent as product width increases.
Registration systems for continuously fed webs are well known but when individual discrete products are being handled, the situation is quite different because here control of any one product does not necessarily constitute control of preceding or succeeding products because each product is independent of all others. Furthermore, products may arrive at the infeed to the machine in an ever changing random spacing. It is also important to note that once a product is released from controlling members of the mechanism, it will travel at the speed of the conveyor upon which it is sitting and its timing cannot be further adjusted or corrected. Furthermore, since there is not connection between the products, each product must be individually controlled, properly spaced and sequenced to enter the space between the conveyor flights.
The Nordstrom patent, U.S. Pat. No. 4,360,098, discloses an infeed conveyor system for feeding packages to a wrapping machine and utilizes a squeeze conveyor that is driven through a differential; the squeeze conveyor running at a speed which is less than synchronous. When product falls behind a synchronous speed, the squeeze conveyor is driven at a speed higher than synchronous which causes the product to catch up and it continues to do so until a sensing mechanism determines that the product is too far advanced and the conveyor then resumes a speed which is slower than synchronous. The difficulty with this particular arrangement is that products are always moving in and out of correct location in the machine, and the product is never being fed at synchronous speed. A further problem is that when a product is sensed to be out of correct location, it is too late to bring it back into correct location. Succeeding products can be gradually brought back into correct location, but the position of the product that was sensed to be out of correct location cannot be corrected. The control conveyor of the apparatus of the present invention, on the other hand, always feeds product at synchronous speed, except for fractional second increases or decreases to bring product back into correct location. In addition, the present invention can correct the position of each product passing through it so that every product is delivered in correct location for subsequent processing.